The present invention relates to a drive roller for feeding an individual substrate, such as an identification card, from a stack of such substrates. The feed roller includes a soft section that supports one surface of a lower substrate in the stack and that provides a high friction surface for positive feeding force, and another harder section that limits compression of the soft section of the roller to control the position of the substrate to effectively limit the size of the outlet from the hopper.
Most printers that print on identification cards feed a bottom card from a stack of cards held in a hopper to the printer. While various developments have been made for restricting the outlet opening from card hoppers, including experimenting with different hardnesses for the feed rollers, problems still persist.
The feed rollers support the card stack so the top edge of the bottom card is below an upper edge of the outlet opening from the hopper. The outlet opening typically will be set to a height of 1xc2xd times the card thickness. For individual cards or stacks with few cards, the setting works. However, as the weight of the stack increases for a full stack of cards, the feed roller compresses, and the bottom card moves down, away from the upper edge of the outlet opening, thereby effectively increasing the vertical size of the outlet opening and resulting in double feed.
A feed roller has to provide a high enough friction force to pull a card from the bottom of a stack, and the high friction roller materials are soft, so the compression of the roller from the weight of the stack is enough so that two cards may be driven under the outlet opening upper edge and through the outlet opening.
If the opening. is set so the height of the opening is 1xc2xd times the card thickness with a full stack of cards, as the stack becomes lighter, the feed roller will be compressed less and the vertical height of the opening will become less than the card thickness to thereby block cards from moving through-the opening.
In the prior art, various neoprene rollers have also been utilized. These harder rollers will not compress so as to allow multiple cards to fit through a controlled opening, but they do not provide enough surface friction to drive cards when the stack is high, for example when in the range of 250 cards. The-cards tend to adhere to each other and the friction between the bottom and next adjacent card may exceed the feed roller drive force.
Isoprene rollers of relative low durometer also have been used, but in conventional arrangements isoprene will compress too much when the weight of the stack is great. The compression may be enough so the outlet of the hopper enlarges enough so more than one card will be fed, or, as explained, if the opening is set with a full stack of cards in place, the opening may close up as the stack reduces in weight.
Card support platforms at the bottom of the stack can be provided with a top portion of a feed roller extending through a slot in the platform to engage a card. The cards have to slide on the platform as they are fed and will tend to be scratched. The platform also has to be very precisely adjusted relative to the target or support plane of the feed roller, which is difficult.
The present invention relates to a drive or feed roller for reliably feeding substrates, such as identification cards, from a hopper containing a stack of such. substrates to a printer. The drive roller has a card driving portion that is relatively low durometer, with a high coefficient friction on its exterior surface and a stiffer or harder smaller diameter section that forms a substrate support to restrict compression of the low durometer section. The high friction section extends for a length along the roller drive axis that is adequate to provide a total force from friction to drive a card that it engages to reliably feed the bottom card. The smaller diameter section comprises at least one disc of slightly smaller diameter than the high friction drive section that will permit the drive section to compress under loads, but only to the size (radius) of the disc. The harder disc or disc section limits the compression of the low durometer drive section, so that the drive section will not compress under the weight of the card stack to an extent that the lower card moves away from the outlet opening upper edge sufficient to permit more than one card to feed through the hopper outlet opening. Alternatively, if the outlet opening is adjusted with a full stack in place, the stack is supported on the hard discs and subsequent expansion of the feed or drive roller as the stack becomes lighter will not be sufficient to reduce the height of the outlet opening to less than the card thickness.
Preferably, the drive roller has the drive section of the soft, high friction material, such as isoprene, in the center, and has two discs, one at each of the opposite ends of the drive section. Both the drive section and the discs are drivably mounted onto a drive shaft. A motor is used for rotating the roller.
Limiting the compression of the softer high friction drive section thus provides for adequate control of hopper outlet size, while the lower durometer elastomeric center section provides adequate friction drive for cards, even when the cards are in a large stack.
Additionally, the drive section of the roller can have a crepe finish (irregular) that increases the overall coefficient of friction of the drive section.
The supporting discs on the roller, which are of slightly smaller diameter than the drive section, can be made of any material that is harder than the drive section and which will not substantially compress. A hard, low friction plastic material such as an acetal resin sold under the trademark/trade name Delrin by E. I. DuPont de Nemours and Company has been found satisfactory for the discs.